In a semiconductor device manufactured from a semiconductor wafer by using a plasma etching apparatus, it is required to form a pattern having a relatively large depth compared to a diameter thereof, e.g., a hole having a high aspect ratio.
In order to form a hole having a high aspect ratio, a target film needs to be sputtered especially by positive ions in the plasma. In that case, as shown in FIG. 12, positive ions 122 remain at a bottom portion of a hole 121 formed in a target film 120 and electrically prevent succeeding positive ions 123 from approaching the bottom portion of the hole 121, which causes the path of the positive ions 123 inside the hole 121 to be changed. Accordingly, the problem such as deformation of the hole 121 or the like may occur.
For that reason, there has been developed a technique for introducing electrons into the bottom portion of the hole (see, e.g., Japanese Patent Application Publication No. 2007-134530). Thus, the positive ions remaining at the bottom portion of the hole are electrically neutralized so that the path of the succeeding positive ions is not varied.
However, along with the trend toward miniaturization of each unit, it is required to form a hole having a high aspect ratio, e.g., a hole having an aspect ratio of about 30 or higher, in a target film. When the hole has an aspect ratio of about 30 or higher, it is difficult to prevent the hole from being deformed even by using the above-described technique.